A new satellite of Uranus

It is stated that whilst observing the occultation of the star SAO 158687 by Uranus on March 10th 1977 an unexpected event was observed suggesting the existence of a hitherto unknown satellite of the planet. The observations were made at the Kavalur Observatory using a near infrared photometer consisting of a refrigerated photocube and Kodak filter attached to the Cassegrain focus of the 102 cm telescope. A very shallow depression of 0.046 magnitude in the light curve of SAO 158687 was observed, as predicted. About 40 min before the mid-point of this dip a sharp drop was observed at 20 h 19 min 38 sec UT, lasting 8.9 sec. This was also visually observed in the guide telescope as a sudden disappearance of the star in the field of view followed by an equally sudden reappearance a few seconds later. A value of 53,000 km was derived for the radius of the satellite orbit, and an approximate period of 9 h 30 min. The size of the body was estimated from the occultation light curve, and from a model of the occultation geometry, and taking into account diffraction near uniform edges, the estimated diameter was about 70 km. The visual magnitude of the satellite was estimated at approximately 19. It is concluded that the body is a new satellite of Uranus. (U.K.)